An apparatus of this type is described in U.S. Pat. No. 3,836,085 dated Sept. 17, 1974. This apparatus has been in commercial operation. Shredded municipal waste may be fed into the tower extractor described in that patent either mechanically by conveyor or pneumatically. The waste material fed to the extractor consists of the product resulting from shredding large volumes of municipal solid wastes or the like to a controlled range of particle sizes. This feed stock constituting urban discard with which the invention deals consists of a wide mixture of materials such as paper, stone, plastic film, glass, metal, textiles, etc. representing a wide variation in particle density. The apparatus utilizes a stream of air to separate the lighter from the heavier constituents.
The previously patented tower extractor proved and established the efficacy of low velocity separation of particles having dissimilar density and shape comprising a shredded heterogeneous matrix. However, the apparatus needed improvement with respect to sharpness of separation, production flow rate and controllability. There was no provision for varying the air flow rate, particularly necessary when the composition of the feed stock changed.